Motor vehicles are customarily equipped with seat occupant detection sensors for use in connection with occupant safety systems including seat belts and pyrotechnically deployed restraints such as air bags. For example, an occupant detection sensor can be used in connection with a seat belt switch to detect an unrestrained seat occupant and trigger an appropriate reminder. Additionally, occupant detection sensors can be used to enable or disable air bag deployment for a particular seating location in the vehicle, and potentially to classify the occupant by seated weight.
A common approach to seat occupant detection involves installing a pressure-responsive sensor on, in or under the bottom foam cushion of the seat, and comparing the measured pressure to calibrated thresholds to detect the presence of an occupant, and possibly distinguish between different classes of occupants. Various types of pressure-responsive sensors have been used for this purpose, including: resistive mats, fluid-filled bladders, and capacitive load cells.